Synthetic fuels processing is a relatively new art. As such, many new and unusual problems have arisen, one of which is the design and fabrication of uniformly distributing manifolds. These manifolds can be used in any place where a large slurry stream must be divided into smaller streams such as before a bank of pumps, heat exchangers or in the passes of a multi-pass furnace. The manifold is particularly used to feed a multi-pass furnace with uniform injection into each pass.
The donor solvent coal liquefaction process, in which these manifolds are used, produces low sulfur liquid products from bituminous, subbituminous, and other types of coal.
A coal preparation section receives feed coal and crushes it to the desired coal particle size for the liquefaction reaction. A slurry drying section mixes the crushed coal with a hydrogenated recycle solvent stream to form the slurry feed to a liquefaction section. Mixing takes place at approximately 250.degree. F. and moisture that enters with the feed coal is vaporized.
In the liquefaction section, the crushed and dried coal is liquefied in a non-catalytic tubular reactor in the presence of molecular H.sub.2 and the hydrogen donor solvent which was added to the slurry dryer. Reactor operating conditions are approximately 840.degree. F. and 1920 psig.
Effluent from the liquefaction reactor is separated by distillation in a product recovery section into gas, naphtha, distillates, and a vacuum bottoms slurry. A portion of the distillates serve as feed to a solvent hydrogenation section. In the solvent hydrogenation section, the solvent is catalytically hydrogenated before being recycled for slurrying with the feed coal. The hydrogen donor solvent is a nominal 400.degree./700.degree. F. boiling range material fractionated from the middle boiling range of the hydrogenated liquid product.
The liquefaction reaction section is comprised of a preheat furnace that heats a mixture of feed from the slurry drier and treat gas, the reactors and a separator vessel. A mixture of coal and solvent is pumped to a high pressure level required for the reactors. Hydrogen rich treat gas is mixed with the feed and both pass through the preheat furnace before entering the reactors. Reactor product then enters the separator drum where lighter material is removed in vapor form overhead and heavier liquids exit via drum bottoms. Heavy intermediate product is sent to fractionation facilities for separation into distillates.
The manifold of this invention feeds the multipass preheat furnace of the liquefaction reaction section, mentioned above. It is necessary to uniformly distribute the coal slurry into each pass of the furnace. However, because the coal slurry is a mixture of coal particles suspended in a hydrocarbon liquid, the ability to uniformly distribute this suspension into each pass is a highly complex task.
The underlying mechanism governing the distribution of the coal at each manifold take-off is a complex combination of inertial, drag, and settling forces which are unique to a given geometry. A potential maldistribution can result from either overall coal concentration differences or particle size distribution variations between passes or a combination of both. Concentration maldistribution resulting from a net inertial or gravitational separation of the coal from the solvent at a manifold take-off point produces variations in the mass fraction of solids between passes. Particle size maldistribution resulting from differences in the balance of forces affecting the large compared to the small particles in the slurry can produce a different coal particle size distribution in each of the manifold passes. Either form of maldistribution will produce significant variations in the overall properties which characterize the slurry flowing in each pass. For example, the pass receiving the higher concentration slurry will have a higher potential for coking and will limit furnace run length. The deviation in properties from design conditions can seriously compromise furnace operability.
Because of the additional complexities of coal/solvent flow dynamics, manifolds for slurry service cannot be designed using the same considerations as for single phase flow. The geometric variables expected to influence slurry distribution include the following:
(a) distribution area--constant or variable PA1 (b) orientation of branch take-off--bottom or side PA1 (c) roundness at branch corner--sharp or smooth
The complexity of the flow at a manifold take-off does not allow a prior judgement of the best combination of these characteristics.